Radio-labeled Nanoparticles for Biomedical Imaging - Nanotechnology for Biomedical Imaging and Diagnostics - page 197

AuNps have been widely used for biomedical imaging owing to their straightforward
preparation and versatile surface chemistry. Lately, cyclic RgD-pegylated AuNp probes
were radiolabeled with 125 I ( 125 I-cRp-AuNps) to target U87mg tumors. Transmission
electron microscope (Tem) images confirmed the localization of 125 I-cRp-AuNps in
α v β 3 -positive U87mg cells and negligible amounts in control α v β 3 -negative mCf7 cells.
SpeCT/CT imaging clearly showed the tumor accumulation 10 min after administration
with high tumor/background contrast (fig. 7.2). Clearance studies showed fast renal
elimination as confirmed by Tem of urine samples. Interestingly, the radiolabeling of 125 I
was directly on the gold surface with good yield and stability [84-86]. There were about
six 125 I isotopes per AuNp with serum stability tests showing more than 85% of 125 I
remaining intact on AuNps after a 24 h incubation at 37°C, indicating the potential of this
AuNp for tumor SpeCT imaging [87].
gNRs have shown promise as theranostic agents owing to their optical properties
and photothermal effect. After conjugation with folic acid and a tyrosine-tagged
peptide, 125 I-labeled folate acid-gold nanorod (fA-gNR) showed clear SpeCT
images at 4 and 24 h p.i in SKOV3 tumor-bearing mice. However, a strong thyroid
uptake signal was observed, indicating dehalogenation of the 125 I from the 125 I-fA-gNR
complex. In vivo photothermal treatment of the tumor was done by illumination with
an 810 nm CW laser (2 W/cm 2 , 600 J/cm 2 ) at 24 h p.i. Tumor ablation was detected in
the 125 I-fA-gNR-treated mice after day 2, and complete obliteration was observed
in 67% of the study group up until day 30 [88].

7.4 Radiolabeled NaNopaRticles foR pet imagiNg

7.4.1 positron-emitting Radionuclides

Among molecular imaging modalities, peT, due to its high sensitivity, quantitative
measurement, limitless depth of tissue penetration, and versatility of chemical probes,
has emerged as a major player in nuclear imaging [89]. positron-emitting radionu-
clide-labeled nanoparticles have been extensively used in both preclinical and clinical
studies as a tool to explore nanoparticles' in vivo pharmacokinetics, imaging capa-
bility, and theranostic potential [35]. for nanoparticles with different physicochemical
properties and functional groups, the peT radionuclide, as well as the radiolabeling
strategy, must be carefully considered to generate an optimal imaging outcome. The
characteristics of commonly used peT radionuclides for nanoparticle labeling are
summarized in Table 7.2.

7.4.2 Radiolabeled liposomes for pet imaging

Liposomes radiolabeled with 64 Cu were used to probe the enhanced permeability and
retention (epR) effect in tumor-bearing mice. In this study, a remote loading approach
was employed to encapsulate 64 Cu into liposomes to achieve improved radiolabeling
stability and tumor accumulation (5.0 ± 2.0% ID/organ) [90]. Due to the long in vivo
half-life ( t 1/2 = 18 h), high tumor-to-muscle ratio (17.9 ± 8.1) was achieved with these
64 Cu-liposomes. In contrast to a small-molecule-based radiotracer of 124 I-SKI212243
targeting egfR kinase, 124 I-SKI212243-conjugated liposomes showed significantly